/**
 * 
 */
package org.mspring.platform.utils;

/**
 * Base64加密解密算法
 * 
 * @author Gao Youbo
 * @since 2012-7-28
 */
public final class Base64 {

    /** No options specified. Value is zero. */
    public final static int NO_OPTIONS = 0;

    /** Specify encoding in first bit. Value is one. */
    public final static int ENCODE = 1;

    /** Specify decoding in first bit. Value is zero. */
    public final static int DECODE = 0;

    /** Do break lines when encoding. Value is 8. */
    public final static int DO_BREAK_LINES = 8;

    /**
     * Encode using Base64-like encoding that is URL- and Filename-safe as
     * described in Section 4 of RFC3548: <a
     * href="http://www.faqs.org/rfcs/rfc3548.html"
     * >http://www.faqs.org/rfcs/rfc3548.html</a>. It is important to note that
     * data encoded this way is <em>not</em> officially valid Base64, or at the
     * very least should not be called Base64 without also specifying that is
     * was encoded using the URL- and Filename-safe dialect.
     */
    public final static int URL_SAFE = 16;

    /**
     * Encode using the special "ordered" dialect of Base64 described here: <a
     * href="http://www.faqs.org/qa/rfcc-1940.html">http://www.faqs.org/qa/rfcc-
     * 1940.html</a>.
     */
    public final static int ORDERED = 32;

    /** Maximum line length (76) of Base64 output. */
    private final static int MAX_LINE_LENGTH = 76;

    /** The equals sign (=) as a byte. */
    private final static byte EQUALS_SIGN = (byte) '=';

    /** The new line character (\n) as a byte. */
    private final static byte NEW_LINE = (byte) '\n';

    private final static byte WHITE_SPACE_ENC = -5; // Indicates white space in
                                                    // encoding
    private final static byte EQUALS_SIGN_ENC = -1; // Indicates equals sign in
                                                    // encoding

    /* ******** S T A N D A R D B A S E 6 4 A L P H A B E T ******** */

    /** The 64 valid Base64 values. */
    /*
     * Host platform me be something funny like EBCDIC, so we hardcode these
     * values.
     */
    private final static byte[] _STANDARD_ALPHABET = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9', (byte) '+', (byte) '/' };

    /**
     * Translates a Base64 value to either its 6-bit reconstruction value or a
     * negative number indicating some other meaning.
     **/
    private final static byte[] _STANDARD_DECODABET = { -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal
                                                                                            // 0
                                                                                            // -
                                                                                            // 8
            -5, -5, // Whitespace: Tab and Linefeed
            -9, -9, // Decimal 11 - 12
            -5, // Whitespace: Carriage Return
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 -
                                                                // 26
            -9, -9, -9, -9, -9, // Decimal 27 - 31
            -5, // Whitespace: Space
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
            62, // Plus sign at decimal 43
            -9, -9, -9, // Decimal 44 - 46
            63, // Slash at decimal 47
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
            -9, -9, -9, // Decimal 58 - 60
            -1, // Equals sign at decimal 61
            -9, -9, -9, // Decimal 62 - 64
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through
                                                          // 'N'
            14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O'
                                                            // through 'Z'
            -9, -9, -9, -9, -9, -9, // Decimal 91 - 96
            26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a'
                                                                // through 'm'
            39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n'
                                                                // through 'z'
            -9, -9, -9, -9, -9 // Decimal 123 - 127
            , -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 128 -
                                                              // 139
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 140 -
                                                                // 152
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 153 -
                                                                // 165
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 166 -
                                                                // 178
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 179 -
                                                                // 191
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 192 -
                                                                // 204
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 205 -
                                                                // 217
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 218 -
                                                                // 230
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 231 -
                                                                // 243
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9 // Decimal 244 - 255
    };

    /* ******** U R L S A F E B A S E 6 4 A L P H A B E T ******** */

    /**
     * Used in the URL- and Filename-safe dialect described in Section 4 of
     * RFC3548: <a
     * href="http://www.faqs.org/rfcs/rfc3548.html">http://www.faqs.org
     * /rfcs/rfc3548.html</a>. Notice that the last two bytes become "hyphen"
     * and "underscore" instead of "plus" and "slash."
     */
    private final static byte[] _URL_SAFE_ALPHABET = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9', (byte) '-', (byte) '_' };

    /**
     * Used in decoding URL- and Filename-safe dialects of Base64.
     */
    private final static byte[] _URL_SAFE_DECODABET = { -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal
                                                                                            // 0
                                                                                            // -
                                                                                            // 8
            -5, -5, // Whitespace: Tab and Linefeed
            -9, -9, // Decimal 11 - 12
            -5, // Whitespace: Carriage Return
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 -
                                                                // 26
            -9, -9, -9, -9, -9, // Decimal 27 - 31
            -5, // Whitespace: Space
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
            -9, // Plus sign at decimal 43
            -9, // Decimal 44
            62, // Minus sign at decimal 45
            -9, // Decimal 46
            -9, // Slash at decimal 47
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
            -9, -9, -9, // Decimal 58 - 60
            -1, // Equals sign at decimal 61
            -9, -9, -9, // Decimal 62 - 64
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through
                                                          // 'N'
            14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O'
                                                            // through 'Z'
            -9, -9, -9, -9, // Decimal 91 - 94
            63, // Underscore at decimal 95
            -9, // Decimal 96
            26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a'
                                                                // through 'm'
            39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n'
                                                                // through 'z'
            -9, -9, -9, -9, -9 // Decimal 123 - 127
            , -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 128 -
                                                              // 139
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 140 -
                                                                // 152
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 153 -
                                                                // 165
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 166 -
                                                                // 178
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 179 -
                                                                // 191
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 192 -
                                                                // 204
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 205 -
                                                                // 217
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 218 -
                                                                // 230
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 231 -
                                                                // 243
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9 // Decimal 244 - 255
    };

    /* ******** O R D E R E D B A S E 6 4 A L P H A B E T ******** */

    /**
     * I don't get the point of this technique, but someone requested it, and it
     * is described here: <a
     * href="http://www.faqs.org/qa/rfcc-1940.html">http://
     * www.faqs.org/qa/rfcc-1940.html</a>.
     */
    private final static byte[] _ORDERED_ALPHABET = { (byte) '-', (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9', (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z', (byte) '_', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z' };

    /**
     * Used in decoding the "ordered" dialect of Base64.
     */
    private final static byte[] _ORDERED_DECODABET = { -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal
                                                                                           // 0
                                                                                           // -
                                                                                           // 8
            -5, -5, // Whitespace: Tab and Linefeed
            -9, -9, // Decimal 11 - 12
            -5, // Whitespace: Carriage Return
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 -
                                                                // 26
            -9, -9, -9, -9, -9, // Decimal 27 - 31
            -5, // Whitespace: Space
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
            -9, // Plus sign at decimal 43
            -9, // Decimal 44
            0, // Minus sign at decimal 45
            -9, // Decimal 46
            -9, // Slash at decimal 47
            1, 2, 3, 4, 5, 6, 7, 8, 9, 10, // Numbers zero through nine
            -9, -9, -9, // Decimal 58 - 60
            -1, // Equals sign at decimal 61
            -9, -9, -9, // Decimal 62 - 64
            11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, // Letters 'A'
                                                                // through 'M'
            24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, // Letters 'N'
                                                                // through 'Z'
            -9, -9, -9, -9, // Decimal 91 - 94
            37, // Underscore at decimal 95
            -9, // Decimal 96
            38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, // Letters 'a'
                                                                // through 'm'
            51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, // Letters 'n'
                                                                // through 'z'
            -9, -9, -9, -9, -9 // Decimal 123 - 127
            , -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 128
                                                                  // - 139
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 140 -
                                                                // 152
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 153 -
                                                                // 165
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 166 -
                                                                // 178
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 179 -
                                                                // 191
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 192 -
                                                                // 204
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 205 -
                                                                // 217
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 218 -
                                                                // 230
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 231 -
                                                                // 243
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9 // Decimal 244 - 255
    };

    public static byte[] decode(byte[] bytes) {
        return decode(bytes, 0, bytes.length, NO_OPTIONS);
    }

    public static byte[] encode(byte[] bytes) {
        return encodeBytesToBytes(bytes, 0, bytes.length, NO_OPTIONS);
    }

    public static boolean isBase64(byte[] bytes) {
        try {
            decode(bytes);
        } catch (InvalidBase64CharacterException e) {
            return false;
        }
        return true;
    }

    /**
     * Returns one of the _SOMETHING_ALPHABET byte arrays depending on the
     * options specified. It's possible, though silly, to specify ORDERED
     * <b>and</b> URLSAFE in which case one of them will be picked, though there
     * is no guarantee as to which one will be picked.
     */
    private static byte[] getAlphabet(int options) {
        if ((options & URL_SAFE) == URL_SAFE) {
            return _URL_SAFE_ALPHABET;
        } else if ((options & ORDERED) == ORDERED) {
            return _ORDERED_ALPHABET;
        } else {
            return _STANDARD_ALPHABET;
        }
    }

    /**
     * Returns one of the _SOMETHING_DECODABET byte arrays depending on the
     * options specified. It's possible, though silly, to specify ORDERED and
     * URL_SAFE in which case one of them will be picked, though there is no
     * guarantee as to which one will be picked.
     */
    private static byte[] getDecodabet(int options) {
        if ((options & URL_SAFE) == URL_SAFE) {
            return _URL_SAFE_DECODABET;
        } else if ((options & ORDERED) == ORDERED) {
            return _ORDERED_DECODABET;
        } else {
            return _STANDARD_DECODABET;
        }
    }

    /* ******** E N C O D I N G M E T H O D S ******** */

    /**
     * <p>
     * Encodes up to three bytes of the array <var>source</var> and writes the
     * resulting four Base64 bytes to <var>destination</var>. The source and
     * destination arrays can be manipulated anywhere along their length by
     * specifying <var>srcOffset</var> and <var>destOffset</var>. This method
     * does not check to make sure your arrays are large enough to accomodate
     * <var>srcOffset</var> + 3 for the <var>source</var> array or
     * <var>destOffset</var> + 4 for the <var>destination</var> array. The
     * actual number of significant bytes in your array is given by
     * <var>numSigBytes</var>.
     * </p>
     * <p>
     * This is the lowest level of the encoding methods with all possible
     * parameters.
     * </p>
     * 
     * @param source
     *            the array to convert
     * @param srcOffset
     *            the index where conversion begins
     * @param numSigBytes
     *            the number of significant bytes in your array
     * @param destination
     *            the array to hold the conversion
     * @param destOffset
     *            the index where output will be put
     * @return the <var>destination</var> array
     * @since 1.3
     */
    private static byte[] encode3to4(byte[] source, int srcOffset, int numSigBytes, byte[] destination, int destOffset, int options) {

        byte[] ALPHABET = getAlphabet(options);

        // 1 2 3
        // 01234567890123456789012345678901 Bit position
        // --------000000001111111122222222 Array position from threeBytes
        // --------| || || || | Six bit groups to index ALPHABET
        // >>18 >>12 >> 6 >> 0 Right shift necessary
        // 0x3f 0x3f 0x3f Additional AND

        // Create buffer with zero-padding if there are only one or two
        // significant bytes passed in the array.
        // We have to shift left 24 in order to flush out the 1's that appear
        // when Java treats a value as negative that is cast from a byte to an
        // int.
        int inBuff = (numSigBytes > 0 ? ((source[srcOffset] << 24) >>> 8) : 0) | (numSigBytes > 1 ? ((source[srcOffset + 1] << 24) >>> 16) : 0) | (numSigBytes > 2 ? ((source[srcOffset + 2] << 24) >>> 24) : 0);

        switch (numSigBytes) {
        case 3:
            destination[destOffset] = ALPHABET[(inBuff >>> 18)];
            destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = ALPHABET[(inBuff >>> 6) & 0x3f];
            destination[destOffset + 3] = ALPHABET[(inBuff) & 0x3f];
            return destination;

        case 2:
            destination[destOffset] = ALPHABET[(inBuff >>> 18)];
            destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = ALPHABET[(inBuff >>> 6) & 0x3f];
            destination[destOffset + 3] = EQUALS_SIGN;
            return destination;

        case 1:
            destination[destOffset] = ALPHABET[(inBuff >>> 18)];
            destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = EQUALS_SIGN;
            destination[destOffset + 3] = EQUALS_SIGN;
            return destination;

        default:
            return destination;
        }
    }

    /**
     * 
     * @param source
     *            The data to convert
     * @param off
     *            Offset in array where conversion should begin
     * @param len
     *            Length of data to convert
     * @param options
     *            Specified options
     * @return The Base64-encoded data as a String
     * @see Base64#DO_BREAK_LINES
     * @throws java.io.IOException
     *             if there is an error
     * @throws NullPointerException
     *             if source array is null
     * @throws IllegalArgumentException
     *             if source array, offset, or length are invalid
     * @since 2.3.1
     */
    private static byte[] encodeBytesToBytes(byte[] source, int off, int len, int options) {

        if (source == null) {
            throw new NullPointerException("Cannot serialize a null array.");
        } // end if: null

        if (off < 0) {
            throw new IllegalArgumentException("Cannot have negative offset: " + off);
        } // end if: off < 0

        if (len < 0) {
            throw new IllegalArgumentException("Cannot have length offset: " + len);
        } // end if: len < 0

        if (off + len > source.length) {
            throw new IllegalArgumentException(String.format("Cannot have offset of %d and length of %d with array of length %d", off, len, source.length));
        } // end if: off < 0

        boolean breakLines = (options & DO_BREAK_LINES) > 0;

        // int len43 = len * 4 / 3;
        // byte[] outBuff = new byte[ ( len43 ) // Main 4:3
        // + ( (len % 3) > 0 ? 4 : 0 ) // Account for padding
        // + (breakLines ? ( len43 / MAX_LINE_LENGTH ) : 0) ]; // New lines
        // Try to determine more precisely how big the array needs to be.
        // If we get it right, we don't have to do an array copy, and
        // we save a bunch of memory.
        int encLen = (len / 3) * 4 + (len % 3 > 0 ? 4 : 0); // Bytes needed for
                                                            // actual encoding
        if (breakLines) {
            encLen += encLen / MAX_LINE_LENGTH; // Plus extra newline characters
        }
        byte[] outBuff = new byte[encLen];

        int d = 0;
        int e = 0;
        int len2 = len - 2;
        int lineLength = 0;
        for (; d < len2; d += 3, e += 4) {
            encode3to4(source, d + off, 3, outBuff, e, options);

            lineLength += 4;
            if (breakLines && lineLength >= MAX_LINE_LENGTH) {
                outBuff[e + 4] = NEW_LINE;
                e++;
                lineLength = 0;
            } // end if: end of line
        } // en dfor: each piece of array

        if (d < len) {
            encode3to4(source, d + off, len - d, outBuff, e, options);
            e += 4;
        } // end if: some padding needed

        // Only resize array if we didn't guess it right.
        if (e <= outBuff.length - 1) {
            byte[] finalOut = new byte[e];
            System.arraycopy(outBuff, 0, finalOut, 0, e);
            // System.err.println("Having to resize array from " +
            // outBuff.length + " to " + e );
            return finalOut;
        } else {
            // System.err.println("No need to resize array.");
            return outBuff;
        }
    }

    /* ******** D E C O D I N G M E T H O D S ******** */

    /**
     * Decodes four bytes from array <var>source</var> and writes the resulting
     * bytes (up to three of them) to <var>destination</var>. The source and
     * destination arrays can be manipulated anywhere along their length by
     * specifying <var>srcOffset</var> and <var>destOffset</var>. This method
     * does not check to make sure your arrays are large enough to accomodate
     * <var>srcOffset</var> + 4 for the <var>source</var> array or
     * <var>destOffset</var> + 3 for the <var>destination</var> array. This
     * method returns the actual number of bytes that were converted from the
     * Base64 encoding.
     * <p>
     * This is the lowest level of the decoding methods with all possible
     * parameters.
     * </p>
     * 
     * 
     * @param source
     *            the array to convert
     * @param srcOffset
     *            the index where conversion begins
     * @param destination
     *            the array to hold the conversion
     * @param destOffset
     *            the index where output will be put
     * @param options
     *            alphabet type is pulled from this (standard, url-safe,
     *            ordered)
     * @return the number of decoded bytes converted
     * @throws NullPointerException
     *             if source or destination arrays are null
     * @throws IllegalArgumentException
     *             if srcOffset or destOffset are invalid or there is not enough
     *             room in the array.
     * @since 1.3
     */
    private static int decode4to3(final byte[] source, final int srcOffset, final byte[] destination, final int destOffset, final int options) {

        // Lots of error checking and exception throwing
        if (source == null) {
            throw new NullPointerException("Source array was null.");
        } // end if
        if (destination == null) {
            throw new NullPointerException("Destination array was null.");
        } // end if
        if (srcOffset < 0 || srcOffset + 3 >= source.length) {
            throw new IllegalArgumentException(String.format("Source array with length %d cannot have offset of %d and still process four bytes.", source.length, srcOffset));
        } // end if
        if (destOffset < 0 || destOffset + 2 >= destination.length) {
            throw new IllegalArgumentException(String.format("Destination array with length %d cannot have offset of %d and still store three bytes.", destination.length, destOffset));
        } // end if

        byte[] DECODABET = getDecodabet(options);

        // Example: Dk==
        if (source[srcOffset + 2] == EQUALS_SIGN) {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1] ] << 24 ) >>> 12 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18) | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12);

            destination[destOffset] = (byte) (outBuff >>> 16);
            return 1;
        }

        // Example: DkL=
        else if (source[srcOffset + 3] == EQUALS_SIGN) {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1 ] ] << 24 ) >>> 12 )
            // | ( ( DECODABET[ source[ srcOffset + 2 ] ] << 24 ) >>> 18 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18) | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12) | ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6);

            destination[destOffset] = (byte) (outBuff >>> 16);
            destination[destOffset + 1] = (byte) (outBuff >>> 8);
            return 2;
        }

        // Example: DkLE
        else {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1 ] ] << 24 ) >>> 12 )
            // | ( ( DECODABET[ source[ srcOffset + 2 ] ] << 24 ) >>> 18 )
            // | ( ( DECODABET[ source[ srcOffset + 3 ] ] << 24 ) >>> 24 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18) | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12) | ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6) | ((DECODABET[source[srcOffset + 3]] & 0xFF));

            destination[destOffset] = (byte) (outBuff >> 16);
            destination[destOffset + 1] = (byte) (outBuff >> 8);
            destination[destOffset + 2] = (byte) (outBuff);

            return 3;
        }
    }

    /**
     * Low-level access to decoding ASCII characters in the form of a byte
     * array. <strong>Ignores GUNZIP option, if it's set.</strong> This is not
     * generally a recommended method, although it is used internally as part of
     * the decoding process. Special case: if len = 0, an empty array is
     * returned. Still, if you need more speed and reduced memory footprint (and
     * aren't gzipping), consider this method.
     * 
     * @param source
     *            The Base64 encoded data
     * @param off
     *            The offset of where to begin decoding
     * @param len
     *            The length of characters to decode
     * @param options
     *            Can specify options such as alphabet type to use
     * @return decoded data
     * @throws IllegalArgumentException
     *             If bogus characters exist in source data
     */
    private static byte[] decode(final byte[] source, final int off, final int len, final int options) {

        // Lots of error checking and exception throwing
        if (source == null) {
            throw new NullPointerException("Cannot decode null source array.");
        } // end if
        if (off < 0 || off + len > source.length) {
            throw new IllegalArgumentException(String.format("Source array with length %d cannot have offset of %d and process %d bytes.", source.length, off, len));
        } // end if

        if (len == 0) {
            return new byte[0];
        } else if (len < 4) {
            throw new IllegalArgumentException("Base64-encoded string must have at least four characters, but length specified was " + len);
        } // end if

        byte[] DECODABET = getDecodabet(options);

        int len34 = len * 3 / 4; // Estimate on array size
        byte[] outBuff = new byte[len34]; // Upper limit on size of output
        int outBuffPosn = 0; // Keep track of where we're writing

        byte[] b4 = new byte[4]; // Four byte buffer from source, eliminating
                                 // white space
        int b4Posn = 0; // Keep track of four byte input buffer
        int i = 0; // Source array counter
        byte sbiDecode = 0; // Special value from DECODABET

        for (i = off; i < off + len; i++) { // Loop through source

            sbiDecode = DECODABET[source[i] & 0xFF];

            // White space, Equals sign, or legit Base64 character
            // Note the values such as -5 and -9 in the
            // DECODABETs at the top of the file.
            if (sbiDecode >= WHITE_SPACE_ENC) {
                if (sbiDecode >= EQUALS_SIGN_ENC) {
                    b4[b4Posn++] = source[i]; // Save non-whitespace
                    if (b4Posn > 3) { // Time to decode?
                        outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn, options);
                        b4Posn = 0;

                        // If that was the equals sign, break out of 'for' loop
                        if (source[i] == EQUALS_SIGN) {
                            break;
                        }
                    }
                }
            } else {
                // There's a bad input character in the Base64 stream.
                throw new InvalidBase64CharacterException(String.format("Bad Base64 input character decimal %d in array position %d", ((int) source[i]) & 0xFF, i));
            }
        }

        byte[] out = new byte[outBuffPosn];
        System.arraycopy(outBuff, 0, out, 0, outBuffPosn);
        return out;
    }
}

class InvalidBase64CharacterException extends IllegalArgumentException {

    InvalidBase64CharacterException(String message) {
        super(message);
    }
}
